# Stream Generation

The `pyETA` GUI initiates a 22-channel[ Lab Streaming Layer](https://labstreaminglayer.org/) (LSL) stream named `'tobii_gaze_fixation'` for real-time eye-tracking analysis. This stream supports gaze tracking and fixation detection, with data sourced from either a `Tobii eye tracker` or a [mock service](https://github.com/moses-palmer/pynput).

***

### Stream Generation

* **Script:** `track.py`
* **Class:** `Tracker`
  * In `application.py`, the `start_stream` method creates a `StreamThread` thread with user-defined parameters and starts it:

    ```python
    self.stream_thread = StreamThread()
    self.stream_thread.set_variables(tracker_params=tracker_params)
    self.stream_thread.start()
    ```
  * `StreamThread` spawns a `TrackerThread`, which instantiates and runs a `Tracker` object from `track.py`.
* **Stream Creation:** When `push_stream=True` (set via GUI checkbox), `Tracker` creates an LSL stream or when `--push_stream` flag is passed in CLI `pyeta track --push_stream`
* **Channel modification:** Combines raw, filtered, and metadata into a 22-channel array.
  * Applies `OneEuroFilter` to raw gaze coordinates.
  * Computes velocity and fixation status using `velocity_threshold`.
  * Produces `left_filtered_gaze_x`, `left_filtered_gaze_y`, `right_filtered_gaze_x` and `right_filtered_gaze_y` used for fixation detection.

<details>

<summary>OneEuroFilter Algorithm</summary>

This algorithm reduces noise and jitters in raw gaze data while preserving responsiveness, which is later used for fixation detection.,

* **Steps:**
  1. **Derivative:** Calculates rate of change:

     ```python
     current_derivative = (current_value - self.previous_value) / time_elapsed
     ```
  2. **Derivative Smoothing:** Applies fixed cutoff (1.0 Hz):

     ```python
     alpha_derivative = self.smoothing_factor(time_elapsed, self.derivative_cutoff)
     filtered_derivative = self.exp_smoothing(alpha_derivative, current_derivative, self.previous_derivative)
     ```
  3. **Adaptive Cutoff:** Adjusts based on velocity:

     ```python
     adaptive_cutoff = self.min_cutoff + self.beta * abs(filtered_derivative)
     ```
  4. **Value Smoothing:** Applies exponential smoothing:

     ```python
     alpha = self.smoothing_factor(time_elapsed, adaptive_cutoff)
     filtered_value = self.exp_smoothing(alpha, current_value, self.previous_value)
     ```

</details>

***

### Stream Properties

* **LSL stream Name:** `'tobii_gaze_fixation'`
* **Channels:** 22

Channel Structure of the stream is described below:

<table><thead><tr><th width="90"></th><th width="225">Channel Name</th><th width="125">Type</th><th width="111">Unit</th><th>Description</th></tr></thead><tbody><tr><td><strong>Left Eye</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>1</td><td>left_gaze_x</td><td>gaze</td><td>normalized</td><td>Raw X gaze position (0-1)</td></tr><tr><td>2</td><td>left_gaze_y</td><td>gaze</td><td>normalized</td><td>Raw Y gaze position (0-1)</td></tr><tr><td>3</td><td>left_pupil_diameter</td><td>pupil</td><td>mm</td><td>Pupil diameter</td></tr><tr><td>4</td><td>left_fixated</td><td>fixation</td><td>boolean</td><td>Fixation status (True/False)</td></tr><tr><td>5</td><td>left_velocity</td><td>velocity</td><td>px</td><td>Gaze velocity</td></tr><tr><td>6</td><td>left_fixation_timestamp</td><td>timestamp</td><td>s</td><td>Time of fixation start</td></tr><tr><td>7</td><td>left_fixation_elapsed</td><td>duration</td><td>s</td><td>Fixation duration</td></tr><tr><td>8</td><td>left_filtered_gaze_x</td><td>filtered_gaze</td><td>normalized</td><td>Smoothed X gaze position</td></tr><tr><td>9</td><td>left_filtered_gaze_y</td><td>filtered_gaze</td><td>normalized</td><td>Smoothed Y gaze position</td></tr><tr><td><strong>Right Eye</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>right_gaze_x</td><td>gaze</td><td>normalized</td><td>Raw X gaze position (0-1)</td></tr><tr><td>11</td><td>right_gaze_y</td><td>gaze</td><td>normalized</td><td>Raw Y gaze position (0-1)</td></tr><tr><td>12</td><td>right_pupil_diameter</td><td>pupil</td><td>mm</td><td>Pupil diameter</td></tr><tr><td>13</td><td>right_fixated</td><td>fixation</td><td>boolean</td><td>Fixation status (True/False)</td></tr><tr><td>14</td><td>right_velocity</td><td>velocity</td><td>px</td><td>Gaze velocity</td></tr><tr><td>15</td><td>right_fixation_timestamp</td><td>timestamp</td><td>s</td><td>Time of fixation start</td></tr><tr><td>16</td><td>right_fixation_elapsed</td><td>duration</td><td>s</td><td>Fixation duration</td></tr><tr><td>17</td><td>right_filtered_gaze_x</td><td>filtered_gaze</td><td>normalized</td><td>Smoothed X gaze position</td></tr><tr><td>18</td><td>right_filtered_gaze_y</td><td>filtered_gaze</td><td>normalized</td><td>Smoothed Y gaze position</td></tr><tr><td><strong>Screen Data</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>19</td><td>screen_width</td><td>screen</td><td>px</td><td>Screen width</td></tr><tr><td>20</td><td>screen_height</td><td>screen</td><td>px</td><td>Screen height</td></tr><tr><td>21</td><td>timestamp</td><td>timestamp</td><td>s</td><td>Data timestamp</td></tr><tr><td>22</td><td>local_clock</td><td>timestamp</td><td>s</td><td>Local system clock</td></tr></tbody></table>

***

### Stream reading for plotting

* **Script:** `reader.py`
* **Class:** `StreamThread`
* Resolves and connects to `'tobii_gaze_fixation'`
* Continuously pulls samples
* Upon requests, gaze data is being parsed.&#x20;

```python
# For gaze data
StreamThread.get_data()

# For fixation data
StreamThread.get_data(fixation=True)
```


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